In a system LSI on which a digital circuit block and an analog circuit block having relatively large power consumption coexist, reduction in power consumption in the analog circuit block has become a major challenge. Particularly, demand for such reduction in power consumption grows for portable equipment. In portable equipment, a power supply of a mounted analog circuit block is turned on/off at an appropriate timing according to the usage state, thereby to reduce power consumption. For example, in a communication system including a transmitter and a receiver, the receiver is halted during transmission while the transmitter is halted during reception.
FIG. 10 is a block diagram illustrating a conventional semiconductor integrated circuit included in such system LSI. In FIG. 10, 801 denotes a reference voltage generation circuit for generating a voltage to be a reference, 802 denotes an analog circuit that is operated using the reference voltage generated in the reference voltage generation circuit 801, and 803 denotes a reference voltage stabilization capacitor for stabilizing an output voltage of the reference voltage generation circuit 801. Further, Pdn denotes a standby signal which turns off the reference voltage generation circuit 801 and the analog circuit 802 when it is “H”, and turns on these circuits when it is “L”. Furthermore, Vr denotes an output of the reference voltage generation circuit 801, and it is stabilized by the reference voltage stabilization capacitor 3 (for example, refer to Japanese Patent No. 3080015 (pages 3 and 4, FIGS. 1 and 3)). FIG. 11 is a waveform chart illustrating a change in the output voltage Vr when the standby signal changes between “L” and “H”. In FIG. 11, tr denotes a recovery time required until the output voltage Vr attains a stable reference voltage Vr0. In the conventional example, as shown in FIG. 11, the time tr is required for charging the reference voltage stabilization capacitor 803 from standby to normal operation, and the time tr causes a delay in recovery.
In the conventional reference voltage generation circuit, the time tr is required for the reference voltage Vr to reach the stable reference voltage Vr0 after canceling of standby, and sometimes a recovery time requested by the system is not satisfied. Especially in a semiconductor integrated circuit having a large reference voltage stabilization capacitor 803, the time required for charging the capacitor increases, resulting in a considerable increase in the recovery time tr.